As illustrated in U.S. Pat. No. 5,507,502, a packing life extended ring assembly includes first and second annular rings, with the second annular ring concentricity encircling the first ring. Both rings have tapered surfaces which mate with one another such that when placed in a stuffing box ahead of packing rings, the tapered rings self adjust during the packing compression process.
As discussed in the above-mentioned patent, slurries, abrasives, dry product and many chemicals can be hard on shaft packing. Even with sufficient flush back pressure, dimensional wear and shaft runout can render packing all but useless in a matter of weeks, or even days. Prior to the two part bushing, the only solution had been to shut down the associated system and repack the stuffing box.
One of the problems with the above-identified system for extending packing life through the utilization of concentric rings is the problem that the tapered surfaces, while adjusting in some measure for bore size and other inconsistent diameters, oftentimes result in the slipping of the inner bushing ring with respect to the outer bushing ring out of their proper position and prior to the gland being tightened down to compress the packing rings between the gland and the bottom of the stuffing box. The result is a canting of the inner ring of the throat. bushing with respect to the outer ring of the throat bushing. This causes two problems. First, with the inner ring canted with respect to the outer ring, it is possible that a void will exist between the bushing and the shaft through which packing material can and does extrude. It will be appreciated that the extrusion of the packing ring material into this space or void results in packing ring failure, to say nothing of the abrasion associated therewith.
Moreover, if the concentric bushing rings are not aligned properly, the canting of one ring with respect to the other itself wears against the shaft sleeve to accelerate sleeve wear.
Thus, not only does packing ring extrusion between the rings and the shaft result in packing ring failure, the misalignment of the concentric rings and the cocking of these rings in the stuffing box upon the compression of the packing rings scores the sleeves and again results in an unsatisfactory arrangement.
Thus, rather than extending packing life, the system of U.S. Pat. No. 5,507,502 can reduce packing life due to the inability of the concentric rings to be held in position during compression and due to uneven pressures associated with the canting.